(a) Field of the Invention
The present invention relates to a shift control system of an automatic transmission and a method thereof.
More particularly, the present invention relates to a shift control system of an automatic transmission and a method thereof that controls hydraulic pressures of an off-going clutch and an on-coming clutch during shifting.
(b) Description of the Related Art
In an automatic transmission provided with a clutch-to-clutch shift system, which is an independent shift system, when up-shifting or down-shifting a shift speed, an off-going clutch is controlled not by controlling a hydraulic pressure of the off-going clutch, but by controlling a time when the hydraulic pressure of the off-going clutch is released. After controlling the time when the pressure of the off-going clutch is released, the hydraulic pressure is released without additional control.
In such an automatic transmission, the hydraulic pressure of the off-going clutch is determined when a hydraulic pressure of an on-coming clutch rises. However, if the hydraulic pressure of the off-going clutch is quickly released or the hydraulic pressure of the on-coming clutch is slowly applied, flare may occur.
In addition, if the hydraulic pressure of the off-going clutch is high in an up-shifting process, problems such as tie-up and deterioration of ride comfort may occur at the early stages of the shifting process.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.